Lactobacillic acid

from Wikipedia, the free encyclopedia
Structural formula
Structure of lactobacillic acid
General
Surname Lactobacillic acid
other names
  • 10- (2-hexylcyclopropyl) decanoic acid
  • 10 - [(1 R , 2 S ) -2-hexylcyclopropyl] decanoic acid
  • (11 R , 12 S ) -Methylene octadecanoic acid
  • cis -11,12-methylenoctadecanoic acid
  • Lactobacillic acid
  • Phytomonic acid
Molecular formula C 19 H 36 O 2
External identifiers / databases
CAS number
  • 19625-10-6 ( cis )
  • 503-06-0 (unspec.)
PubChem 656761
Wikidata Q2823275
properties
Molar mass 296.49 g mol −1
Physical state

firmly

Melting point

27.8-28.8 ° C

solubility

soluble in acetone , chloroform , diethyl ether and petroleum ether

safety instructions
GHS hazard labeling
no classification available
As far as possible and customary, SI units are used. Unless otherwise noted, the data given apply to standard conditions .

The Lactobacillsäure ( English lactobacillic acid ), science-10- (2-Hexylcyclopropyl) decanoic acid, is a naturally occurring chemical compound from the group of fatty acids . Other synonyms include lactobacillic acid and phytomonic acid . The salts are called lactobacillates. A special feature is the cyclopropane ring in the carbon chain . In addition, lactobacillic acid with 19 carbon atoms is one of the fatty acids with an uneven number of carbon atoms.

The fatty acid was detected in bacteria of the genus Lactobacillus in the 1950s , but is also found in numerous other types of bacteria. The bacterial biosynthesis of lactobacillic acid takes place from cis - vaccenoic acid ( cis -11-octadecenoic acid), an unsaturated fatty acid that has one less carbon atom. Bacteria in a batch culture form the fatty acid at the end of the exponential phase of growth or in the early stationary phase of growth. Previous studies show that the biosynthesis and storage of lactobacillic acid in the cell membrane is associated with a protective effect for the bacterial cells , without the exact mechanism being finally clarified. In bacteriology , the fatty acid is primarily used for analytical purposes, for example in the identification of bacteria.

history

discovery

In the 1950s researched a working group of the University of Pittsburgh to bacteria of the genus Lactobacillus , the biotin as a growth factor need. It was already shown beforehand that biotin is no longer necessary for the growth of bacteria if certain fatty acids are instead present in the nutrient medium . When investigating the influence of biotin on fatty acid metabolism , the researchers initially concentrated on the species Lactobacillus arabinosus , which is listed as Lactobacillus plantarum according to the current system . They cultivated the bacteria in a semi-synthetic nutrient medium, harvested the cells and extracted the “free” lipids with acetone and diethyl ether . This fraction makes up about 20% of the total lipids. In order to obtain the “bound” lipids, an acid hydrolysis was then carried out, during which fatty acids bound as esters were released and also extracted with diethyl ether.

The fatty acids were methylated with diazomethane to give the methyl esters and separated according to their boiling points using fractional distillation . Based on the distillation curve, the presence of esters of the C 16 , C 18 and C 19 fatty acids was expected. The fatty acid obtained from the C 19 fraction had a melting point of 28-29 ° C. after purification by recrystallization . The compound was investigated using numerous physical and chemical methods and its molecular formula was determined as C 19 H 36 O 2 . In 1950 this was only the second fatty acid with 19 carbon atoms to be isolated from microorganisms. 1929 was tuberculostearic ( English tuberculostearic acid , molecular formula C 19 H 38 O 2 ) discovered that out of the TB germs can Mycobacterium tuberculosis was isolated. In analogy to their names, the biochemists suggested the English name lactobacillic acid , since the fatty acid came from a Lactobacillus species. Lactobacillic acid could also be isolated from Lactobacillus casei . In the publication, the scientists emphasized the effects of their discovery, which contradicted the opinion at the time that only fatty acids with an even number of carbon atoms occur in nature.

"The discovery in two lactobacilli of a fatty acid containing 19 carbon atoms raises some rather fundamental points and is in marked contrast to the accepted concept that the fatty acids of animal and plant tissues are mainly of the even carbon chain variety."

"The discovery of a fatty acid with 19 carbon atoms in two Lactobacillus species raises some fundamental questions and is in clear contrast to the accepted view that the fatty acids in animal and plant tissue mainly belong to the type of even-numbered carbon chains."

- K. Hofmann, RA Lucas, SM Sax : The chemical nature of the fatty acids of Lactobacillus arabinosus

Structure elucidation

Reaction scheme for the hydrogenation of lactobacillic acid: The hydrogenation of lactobacillic acid (1) with hydrogen (H 2 ) results in several hydrogenation products: cleavage of bond 1 (red) leads to nonadecanoic acid (2), cleavage of bond 2 (blue) or 3 (green) ) leads to a mixture of methyloctadecanoic acids (3), (4).

The “free” and “bound” lipids do not differ significantly in their fatty acid composition. In addition to lactobacillic acid with a proportion of 31%, it also contains palmitic acid (C16: 0), stearic acid (C18: 0) and cis - vaccenic acid (C18: 1 cis -11) with a proportion of 37, 2 and 20%. The test results of the newly discovered fatty acid showed that it is a saturated fatty acid . It is stable to oxidizing agents that would react with a double bond in the carbon chain. In the reaction with hydrogen bromide (HBr), however, is done addition of HBr in the molecule . Also, a hydrogenation is possible, besides arise several isomeric fatty acids having the empirical formula C 19 H 38 O 2 , one of which was as nonadecanoic be identified. The other compound is a branched-chain fatty acid with a methyl group as a branch (methyloctadecanoic acid ), although at the time the scientists could not distinguish whether one or more isomers were present. Based on the results of the chemical and physical ( infrared spectroscopy and X-ray diffractometry ) methods for structure elucidation , a saturated fatty acid was proposed as the structure, which has a cyclopropane ring in the carbon chain. The cyclopropane ring reacts with the opening of the ring with hydrogen bromide and also with hydrogen during the hydrogenation (see illustration of the reaction scheme) without a double bond being present.

Suggestion of the structural formula of lactobacillic acid (1953)

After the discovery of lactobacillic acid in the lipids of Lactobacillus arabinosus , Klaus Hofmann's working group continued its research on Lactobacillus casei and was also able to isolate the fatty acid from its lipids. By comparison with synthetic fatty acids they could determine the position of the cyclopropane ring and proposed to refer 11,12-Methylenoctadecansäure ( english 11,12-methyleneoctadecanoic acid ) before, without regard to the stereoisomerism define the structure. The term methylene refers to the methylene group and can also be used for ring members in cycloalkanes . The numbers serve as locants and describe the position of the cyclopropane ring. Viewed from the carboxy group , the carbon atoms at positions 11 and 12 are part of the cyclopropane ring, the third carbon atom of which - together with the hydrogen atoms attached to it - is included in the name as methylene.

cis - trans isomerism of lactobacillic acid; above the cis isomer, below the trans isomer

Viewed from the cyclopropane ring, there are different substituents on two carbon atoms , so that there is a cis - trans isomerism (see figure). The substituents can be on the same side ( cis ) or on different sides ( trans ) of the ring bond. Hofmann et al. a. do not clarify at first upon discovery. However, in 1954 they hypothesized that the cis isomer was present. This was confirmed in 2005 by a Canadian research group. A clear description of the spatial arrangement of the substituents is using the Cahn-Ingold-Prelog Convention possible, according to this, the absolute configuration of the molecule than 11 R , 12 S indicated. The name (11 R , 12 S ) -methylene octadecanoic acid derived from this is common, even if it does not correspond to the recommendations of the IUPAC nomenclature . For the systematic naming of lactobacillic acid, the absolute configuration is given from the cyclopropane ring, with a C 6 substituent (hexyl group) and a C 10 substituent containing the carboxy group ( decanoic acid ), so that 10 - [(1 R , 2 S ) -2-hexylcyclopropyl] decanoic acid is obtained.

etymology

Lactobacillic acid and lactobacillic acid are translations of the English name lactobacillic acid , which the scientists suggested in a Lactobacillus species when they discovered this fatty acid (1950) . The term lactobacillic acid occurs more frequently than lactobacillic acid in the German-language literature. As early as 1938 was from a different research group an unusual fatty acid from the bacterium Agrobacterium tumefaciens (at that time as a bacterium tumefaciens or Phytomonas tumefaciens isolated and after the genus name as designated) Phytomonsäure ( English phytomonic acid ), respectively. According to the knowledge of the scientists at the time, this saturated fatty acid had the molecular formula C 20 H 40 O 2 . A branched-chain fatty acid having a methyl group as a branch, methylnonadecanoic acid, has been proposed as a structure. However, K. Homann et al. a. 1955 show that this compound isolated from Phytomonas tumefaciens is actually lactobacillic acid. According to her, the substance originally investigated had been contaminated. The names lactobacillic acid and phytomonic acid are used both for the compound with and without specifying the absolute configuration.

Occurrence

Occurrence of lactobacillic acid

After the discovery of lactobacillic acid in the lipids of Lactobacillus arabinosus , Klaus Hofmann's working group was also able to determine this fatty acid with a content of 16% in the lipids of Lactobacillus casei . It is also found in L. acidophilus , L. buchneri , L. delbrueckii subsp. bulgaricus , L. delbrueckii subsp. lactis , L. fermentum and L. helveticus with a content of 10 to 30% have been detected. However, lactobacillic acid is not restricted to representatives of the genus Lactobacillus or lactic acid bacteria in general. The fatty acid was also detected in higher proportions (10–20%) in gram-negative bacteria such as Agrobacterium tumefaciens and Escherichia coli , and in smaller amounts (5–10%) in Serratia marcescens , Klebsiella aerogenes and Pseudomonas fluorescens . Also Brucella TYPES contain Lactobacillsäure, as Bordetella species, however, the content is only 1-2%.

Lactobacillic acid occurs in both gram-positive and gram-negative bacteria; the occurrence extends to strictly aerobic , microaerophilic , facultative and strictly anaerobic genera. Although the fatty acid is widespread in bacteria, it is not found in all genera. Bacteria that do not have any unsaturated fatty acids in the membrane lipids also do not have any lactobacillic acid. This is particularly true of thermophilic bacteria and archaea . In contrast, the fatty acid is rarely found in eukaryotic organisms . It is contained in rapeseed oil , for example , which contains little erucic acid (so-called LEAR varieties).

Occurrence of other cyclopropane fatty acids

The biosynthesis and occurrence of lactobacillic acid is closely related to dihydrosterculic acid (compare sterculic acid ), which is also a saturated fatty acid with the empirical formula C 19 H 36 O 2 , which contains a cyclopropane ring. Here, however, the ring is located at positions 9 and 10 of the carbon chain, hence it is also referred to as cis -9,10-methylenoctadecanoic acid. Dihydrosterculic acid is also found in the lipids of many bacterial genera , but was also found in eukaryotes, for example in protozoa from the group of the Trypanosomatida , here in the genera Crithidia , Leishmania , Leptomonas , Herpetomonas and Phytomonas . According to a study published in 2014, lactobacillic acid and dihydrosterculic acid are also found in very small amounts (<0.1% of total fatty acids) in cow milk , but not in goat or sheep milk .

Extraction and presentation

extraction

Lactobacillic acid can be isolated from the lipids of the bacteria, as used by the working group for the discovery. Initially, the phospholipids or triglycerides are hydrolysed ( saponified ) , during which the fatty acid bound as an ester is released. Since there are other fatty acids in addition to lactobacillic acid, they are then separated using urea extractive crystallization or column chromatography . The fractional crystallization process can also be used.

Chemical synthesis

The chemical synthesis is similar to the biosynthesis starting from the unsaturated compound without cyclopropane ring, the vaccenic acid . In a Simmons-Smith reaction , a carbene is added to the double bond of the unsaturated fatty acid; diiodomethane and zinc are used to form the carbene . The Simmons-Smith reaction is stereospecific ; cis -11-octadecenoic acid ( cis -vaccenic acid) is used for the preparation of cis -11,12-methylenoctadecanoic acid (lactobacillic acid). This can be of natural origin or can be synthesized from 11-octadecinic acid.

Biosynthesis in bacteria

Biosynthesis of lactobacillic acid: S-adenosylmethionine SAM (1) provides the methylene group for cis - vaccenic acid (2); the reaction mechanism proceeds via the formation of a carbocation (3); from this lactobacillic acid (4) is formed, while SAM is hydrolyzed to homocysteine (5) and adenosine (6); the "R" for the fatty acids shows that they are not free, but z. B. are bound in phospholipids.

The main features of the biosynthesis of lactobacillic acid were already cleared up in 1961. The Lactobacillsäure, as well as other naturally occurring cyclopropane fatty acids ( English cyclopropane fatty acids are also abbreviated CFA or CPFA) from the corresponding unsaturated fatty acids formed which have less of a carbon atom and exhibit on the cyclopropane ring cis -configuration. The precursor of the Lactobacillsäure ( cis is -11,12-Methylenoctadecansäure) thus the cis -Vaccensäure ( cis -11-octadecenoic acid). This was accomplished with the carbon isotope 14 C labeled shown precursors.

With the aid of the enzyme cyclopropane fatty acid synthase ( EC  2.1.1.79 ), a methylene group is added to the double bond of cis -vaccenic acid. The methylene group is derived from S- adenosylmethionine . The unsaturated fatty acid is not free, but is bound as an ester within phospholipids . The reaction mechanism takes place via the formation of a carbocation . The enzyme only catalyzes the reaction in the case of unsaturated fatty acids whose double bond has a cis configuration; the corresponding trans isomers are not converted.

When the bacteria are cultivated in a batch culture, the formation of the CFA occurs suddenly at a specific point in time rather than its concentration increasing steadily. At the same time, the decrease in the concentration of unsaturated fatty acids (as a preliminary stage) is observed. The formation of the cyclopropane fatty acid takes place at the end of the exponential phase of growth or in the early stationary growth phase .

Biological importance

Physiological importance for bacteria

Since lactobacillic acid was discovered in bacteria that require biotin as a growth factor , studies were initially carried out on these bacteria in the 1950s. With Lactobacillus plantarum (then L. arabinosus ), L. casei and L. delbrueckii it was found that they can grow without biotin if the nutrient medium contains lactobacillic acid. L. acidophilus , for which biotin is not essential , is promoted in growth by lactobacillic acid. It is now known that biotin is an important component of various enzymes involved in lipid metabolism , e.g. B. the acetyl-CoA carboxylase and propionyl-CoA carboxylase . It was also recognized at that time that several saturated fatty acids have inhibitory (inhibiting) effects on bacterial growth, but that this effect is canceled out by lactobacillic acid and some unsaturated fatty acids. Since then, several studies have shown that the synthesis of lactobacillic acid is an advantage for the corresponding bacteria in order to adapt to unfavorable environmental conditions. Examples of this are suboptimal or even extreme temperatures, a falling pH value in the medium or the entry into the stationary growth phase.

The importance of the cyclopropane fatty acid synthesis is still the subject of research. To this end, there was a study of mutants of E. coli , which the CFA gene is missing, which synthase cyclopropane fatty acid for the enzyme encoded . The lack of the enzyme has no negative impact on growth and the bacteria do not show any phenotypic differences, with the exception that lactobacillic acid or other cyclopropanoic acids do not appear among the fatty acids present. A similar experiment was performed with artificially made mutants of Brucella abortus . The bacteria are still able to multiply in macrophages , so lactobacillic acid has no influence on the intracellular life cycle. However, if the bacteria are cultured in a nutrient medium that has a low pH and high osmolarity , less growth can be observed compared to the unchanged cells. These conditions can be transferred to the survival of Brucella abortus in the environment, an acidic environment with high osmolarity can also occur there. The mutants that do not form lactobacillic acid have poorer chances of survival there and consequently cannot be transferred to a host as easily as is the case, for example, with a smear infection . The investigation of the promoter of the cfa gene also shows that the expression is promoted by low pH and high osmolarity, i.e. the enzyme CFA synthase is formed under these conditions.

From the point of view of energy metabolism , the formation of the cyclopropane ring in lactobacillic acid means a relatively high expenditure of energy for the cell. The S- adenosyl methionine, which acts as a transmitter for the methylene group, then has to be regenerated from S- adenosyl homocysteine. This is associated with the hydrolytic cleavage of three ATP molecules per molecule . It was therefore assumed that the cyclopropane ring serves as a memory for an activated methylene group in order to later enable subsequent methylation reactions. This is contradicted by the fact that at least in E. coli the lactobacillic acid content remains constant. The time of the biosynthesis suggests that the fatty acid has a protective effect on the bacterial cells in the following stationary phase. What exactly this protective effect consists of has not yet been clarified despite intensive research.

The composition of the fatty acids in the phospholipids of the cell membrane influences their fluidity . An exchange of cis -vaccenic acid by lactobacillic acid has different effects, depending on the position of the glycerol at which the fatty acid is esterified in the phosphoglyceride . Within the temperature range that is relevant for most living things, the incorporation of a fatty acid with a cyclopropane ring tends to mean that a change in temperature does not have a major influence on the fluidity. The biomembrane is therefore fluid over a somewhat larger temperature range. Contrary to what the contained structure of the cyclopropane suggests, lactobacillic acid - bound in the phospholipids - is relatively stable. Compared to unsaturated fatty acids (as a preliminary stage in biosynthesis), it is even more stable with regard to mild oxidizing agents, such as treatment with ozone ( ozonolysis ) or with photochemically formed singlet oxygen . Some researchers interpret this to mean that the incorporation of lactobacillic acid in the cell membrane does not have any significant influence on the physical properties of the membrane, but its chemical properties are changed as a result, which is an advantage for the organism.

An example of a useful effect of lactobacillic acid is given by Oenococcus oeni . The lactic acid bacterium is used in winemaking to convert malic acid into lactic acid during malolactic fermentation , which in turn is converted into ethanol by yeasts . This will reduce the acidity of the wine. It is Oenococcus oeni relatively high concentrations exposed to ethanol in the alcoholic fermentation is produced by yeasts. Investigations of the cell membrane of the bacterium showed that the rate of biosynthesis of phospholidides increases with increasing ethanol concentration in the surrounding nutrient medium. In addition, more lactobacillic acid is formed in the membrane lipids, while the content of cis -vaccenic acid decreases. This is interpreted as a protective mechanism against the toxic effects of ethanol. The formation of lactobacillic acid helps the bacterium to adapt to the unfavorable environmental conditions. A similar protective effect was found in L. delbrueckii subsp. bulgaricus discovered. It shows improved survivability compared to freeze-drying when there is more lactobacillic acid in the cell membrane.

The probiotic effect of Lactobacillus reuteri is attributed to immunomodulating substances that inhibit the production of the cytokine TNF ( tumor necrosis factor ) in humans. The examination of the membrane lipids of different strains of Lactobacillus reuteri shows that only the TNF-inhibiting strains contain lactobacillic acid. Here, too, the cfa gene was inactivated in a lactobacillic acid-producing bacterial strain and the mutants were cultivated in the experiment. The supernatant was tested in a cell culture and, in contrast to the supernatant of the wild type, suppressed the production of TNF. However, adding lactobacillic acid as a pure substance does not inhibit cytokine production. Thus, the fatty acid is only indirectly involved in the immunomodulating activity of L. reuteri , a possible explanation given is an altered membrane fluidity.

Classification and identification of bacteria

With the development of instrumental methods for fatty acid analysis, the detection of different fatty acids in bacteria has become a common test feature since the 1970s. The fatty acid patterns are often used for taxonomic classification, since related species often have a similar composition of the fatty acids in the lipids. The pattern of fatty acid distribution can be used to distinguish Brucella and Bordetella species from one another. Research results from 2013 show that the occurrence of lactobacillic acid in Brucella canis depends on the geographical origin of the bacterial strains and indicate that only strains pathogenic to humans contain this fatty acid. The examination of the fatty acid pattern including lactobacillic acid and other cyclopropane fatty acids is also suitable for differentiating between Weissella species and other lactic acid bacteria.

proof

The detection as well as the quantitative determination of lactobacillic acid is carried out - as is usual with fatty acids - by gas chromatography of the methyl ester, often as gas chromatography with mass spectrometry coupling (GC / MS). Because of the cyclopropane ring, however, a suitable methylation reagent must be used. For example, hydrogen chloride in anhydrous methanol is not suitable , since this reagent can react with the cyclopropane ring, in which case a branched-chain fatty acid with a methoxy group is formed. In contrast, sodium methoxide in anhydrous methanol is well suited , as is sodium hydroxide or potassium hydroxide in methanol. The formation of 3-pyridylmethyl esters (picolinyl esters) with nicotinyl alcohol (pyridyl methanol) is recommended, particularly for structural elucidation with the aid of mass spectrometry .

Individual evidence

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  2. ↑ This substance has either not yet been classified with regard to its hazardousness or a reliable and citable source has not yet been found.
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literature

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